359 
of this need. Some of the more interesting facts are particularly well 
exemplified in our orchids, to the philosophic study of which Darwin’s 
important work “On the Fertilization of Orchids” gave a distinct 
impulse. But here we have adaptation of the plant only, and with 
scarcely an exception most flowers, including those of our orchids, may 
be fertilized by different insects. There are, in fact, few which are 
dependent on a single species for pollination, and, so far as I know, 
our yuccas furnish the only instance of this kind. It is to the fertili- 
zation of these plants that I would first draw your attention. 
The Yuceas (Fig. 57) area characteristic American group of liliaceous 
Fig. 57.—Flower of Yucca aloifolia fully opened. 
plants, finding their home more particularly in the southern United 
States and Mexico. There are many species which have been divided 
even into subgenera by Dr. Engelmann, as Sarcoyucca, Clistoyucea, 
Chenoyucca, and Hesperoyucca; but for our present purpose they may 
all be included under the one gonus Yucca, as they all possess certain 
characteristics in common, viz, a thick, submucilaginous root, which is in 
reality a subterranean stem; lance-shaped, evergreen leaves, narrow or 
broad, rigid or flaccid, and with the edge either filamentose, smooth, or 
more or less distinctly serrate. The leaves produce a coarse fiber, val- 
uable for certain kinds of fabrics, while the trunks of the tree Yuccas 
have been used to make the toughest kind of paper. The fruit of some 
species, as of aloifolia and baccata, is fleshy and edible. Itis, however, 
the flowers to which I would draw more especial attention. They are 
produced in large panicles, and are characterized, as a rule, by the 
authers not reaching anywhere near the stigma, so that fertilization 
unaided can take place only by the merest accident. The Yuecas show 
great variation in detail, both in leaf, general habitus, flower-stalk, flower 
